This invention relates to a process for treating washing liquor from the gas main of coke ovens to obtain both an aqueous liquid substantially tar and solid-free which is suitable for reuse as the washing liquid in the gas main and to obtain tar having a low water and a low solids content.
Most coke ovens presently in operation include a widegas main extending along the oven battery for conducting gases liberated in the distillation process from the coking chambers. A negative pressure is developed in the gas main to withdraw and conduct the gases along the gas main. In the gas main, sufficient quantities of water trickle through the gas stream to considerably reduce the temperature of the gas and to separate out various constituents of the gas, particularly tar and solids. The materials removed from the gas by the water are carried in the form of a washing liquor which flows along the bottom of the gas main. It is essential and the usual practice to remove the tar and solid ingredients present in the gas main washing liquor before the liquid is returned to the gas main to wash additional quantities of gas. In the separation process, the tar yield should have a very low solids content for convenience of storage of the tar and a very low water content to facilitate further processing of the tar.
Equipment known in the art for treating such flushing liquor is very large and the separation process requires a relatively long period of time. Moreover, the separation process is often unsatisfactory because unacceptable quantities of solids and water remain in the tar. To intensify the separation process, which is based on gravity, the width or length of the tanks used for the separation process must be increased correspondingly. Thus, more floor space is needed and capital investment costs are considerably increased.
In modern coke oven batteries, the trend is for an increase in the solids content in the gas passed into the gas main and, therefore, the solids content of the washing liquid and tar is also increased. As the carbonization time by a coke oven battery is reduced, changes occur to the composition of the tar including an increased quantity of pitch. The treating process for the mixture of water, tar and solids yielded from gas mains of modern coke oven batteries is an undertaking which has become increasingly difficult and more expensive.
Endeavors to alleviate the above disadvantages include gravity settling processes wherein the gas main washing liquor is separated into water, low solids tar and high solids or thick tar by a gravity in a tar separator. In other known processes, the washing liquor is passed seriatium through a preliminary separator, for separating large lumps of thick tar therefrom, and then through a tar separator wherein the washing liquor is separated into water, tar and thick tar phases. The tar can then be passed through another separator wherein, as in all the facilities hereinbefore mentioned, there is considerable gravity separation of water and solids from the tar. Thereafter, the tar is frequently subjected to further dewatering in large heated settling and storage tanks. In other known processes, the tar received from each gravity separator is passed into a decanting centrifuge for separation of the solids therefrom before the tar is passed into the storage tank.